/Engine/Plugins/Runtime/GameplayAbilities/Source/GameplayAbilities/Public/GameplayEffect.h
Attempts to calculate the magnitude given the provided spec. May fail if necessary information (such as captured attributes) is missing from the spec.
True if the calculation was successful, false if it was not
bool AttemptCalculateMagnitude ( const [FGameplayEffectSpec](API\Plugins\GameplayAbilities\FGameplayEffectSpec) & InRelevantSpec, float & OutCalculatedMagnitude, bool WarnIfSetByCallerFail, float DefaultSetbyCaller ) const